Tributyltin hydride reaction

Tributyltin hydride, reaction with alkyl halides. 358 Tricarboxylic acid cycle, see Citric acid cycle... 

Intramolecular radical addition of the dimethylallyltrichloro acetate 180 affords a trichloro lactone, 181 whose excessive chlorine atoms are eliminated by tributyltin hydride, (Reaction scheme 113) [274, 275]. 

The hydrogenolyaia of cyclopropane rings (C—C bond cleavage) has been described on p, 105. In syntheses of complex molecules reductive cleavage of alcohols, epoxides, and enol ethers of 5-keto esters are the most important examples, and some selectivity rules will be given. Primary alcohols are converted into tosylates much faster than secondary alcohols. The tosylate group is substituted by hydrogen upon treatment with LiAlH (W. Zorbach, 1961). Epoxides are also easily opened by LiAlH. The hydride ion attacks the less hindered carbon atom of the epoxide (H.B. Henhest, 1956). The reduction of sterically hindered enol ethers of 9-keto esters with lithium in ammonia leads to the a,/S-unsaturated ester and subsequently to the saturated ester in reasonable yields (R.M. Coates, 1970). Tributyltin hydride reduces halides to hydrocarbons stereoselectively in a free-radical chain reaction (L.W. Menapace, 1964) and reacts only slowly with C 0 and C—C double bonds (W.T. Brady, 1970 H.G. Kuivila, 1968). 

The /3,7-unsaturated aldehyde 407 is prepared in good yields by the carbo-nylation of an allylic chloride under mild conditions using tributyltin hydride as a hydride source[261]. Aldehydes are obtained in moderate yields by the reaction of CO and H2[262],... 

Alkyl halides can be reduced to alkanes by a radical reaction with tributyltin hydride, (C4H9)3SnH, in the presence of light (hv). Propose a radical chain mechanism by which the reaction might occur. The initiation step is the light-induced homolytic cleavage of the Sn— H bond to yield a tributyltin radical. 

The reaction of 5-chloro-l,4-benzoxazepine (4), whose preparation is described below, with tributyltin hydride catalyzed by tetrakis(triphenylphosphane)palladium(0) gives 1,4-benzox-azepine (5).32... 

Radical Diels-Alder reactions have been used mainly to synthesize polycyclic molecules. These reactions, like those that involve cations and anions as components, proceed quickly but generally do not give high yields. Thus, the tricyclic enone 14 is the result of an intramolecular Diels-Alder reaction of quenched vinyl radical intermediate 13 obtained by treating the iododienynone 12 with n-tributyltin hydride/2,2 -azobisisobutyronitrile (AIBN) [28] (Equation 1.11). 

The reaction of tributyltin hydride with ring-substituted benzyl chlorides gives a Hammett p-factor of -1-0.81, confirming the "nucleophilic character of the BusSn- radical (303). 

Our group has also reported that the alkylation products of 4-cyano-l,3-diox-anes can serve as substrates for radical atom transfer reactions [41]. One such example is shown below (Eq. 17). Slow addition of tributyltin hydride/AIBN to a refluxing solution of cyanohydrin 115 generated the radical nitrile transfer product 116. This method, though somewhat limited in scope, can provide access to syn-l,3-diols which maybe unstable to the vigorous Li/NHg reduction conditions. 

Quebrachitol was converted into iL-c/j/roinositol (105). Exhaustive O-isopropylidenation of 105 with 2,2-dimethoxypropane, selective removal of the 3,4-0-protective group, and preferential 3-0-benzylation gave compound 106. Oxidation of 106 with dimethyl sulfoxide-oxalyl chloride provided the inosose 107. Wittig reaction of 107 with methyl(triphenyl)phos-phonium bromide and butyllithium, and subsequent hydroboration and oxidation furnished compound 108. A series of reactions, namely, protection of the primary hydroxyl group, 0-debenzylation, formation of A-methyl dithiocarbonate, deoxygenation with tributyltin hydride, and removal of the protective groups, converted 108 into 7. 

Zard and coworkers [32] reported a simple approach to create another group of natural products, namely the lycopodium alkaloids [15]. These authors first investigated the reaction of O-benzoyl-N-allylhydroxylamide 3-60 with tributyltin hydride and ACCN in refluxing toluene, which led (after formation of the N-radical 3-61 in a 5-exo-trig/5-exo-trig cyclization) to the undesired pyrrolidine 3-62 in 48% yield. Nevertheless, a small structural modification, namely the placement of a chlorine atom at the allyl moiety as in 3-63, induced a 5-exo-/G-endo- instead of the 5-exo-/5-... 

The [6.5.5]-ring fused tricyclic motif is found in many natural products, and has therefore become an important target in synthesis. A convenient access to this structural framework is offered by a radical domino procedure published by the Nagano group [41]. This reaction of optical pure dibromoacetal 3-85 led to the desired tricycle 3-87 via 3-86 as a single diastereoisomer in a very respectable yield of 94% by applying classical radical conditions (excess tributyltin hydride/AIBN, irradia-... 

The connection of radical and pericyclic transformations in one and the same reaction sequence seems to be on the fringe within the field of domino processes. Here, we describe two examples, both of which are highly interesting from a mechanistic viewpoint. The first example addresses the synthesis of dihydroindene 3-326 by Parsons and coworkers, starting from the furan 3-321 (Scheme 3.79) [128]. Reaction of 3-321 with tributyltin hydride and AIBN in refluxing toluene led to the 1,3,5-hexatriene 3-324 via the radicals 3-322 and 3-323. 3-324 then underwent an elec-trocyclization to yield the hexadiene 3-325 which, under the reaction conditions, aromatized to afford 3-326 in 51 % yield. 

One of the very rare examples of a combination of a radical with a pericydic reaction - in this case a [4+2] Diels-Alder cycloaddition - is depicted in Scheme 3.83 [133]. The sequence, elaborated by Malacria and coworkers, is based on the premise that the vinyl radical 3-341 formed from the substrate 3-340 using tributyltin hydride exists mainly in the Z -form. This is reduced by a hydrogen atom to form a 1,3-diene, which can undergo an intramolecular Diels-Alder reaction via an exotransition state reaction (the chain lies away from diene). 

In variations of the above reaction, the selenoesters 113 and 115 are cyclized to the indolonaphthyridines 114 and 116 (Equations 24 and 25) <2005JOC9077>, and carbazolonaphthyridines such as 119 may be prepared by cycliza-tion of either 117 or 118 with tributyltin hydride (Scheme 33) <2005T9102>. 

Reaction of an A-(o-halogcnobenzoyl)pyridoindole 360 with tributyltin hydride and azobis(cyclohexanecarbonitrile) gives the /vrr -fused pyrrolonaphthyridine 361 along with the (6 5 6) pyridoindolizine 362 (Equation 129). Compound 361 is obtained by the action of tributyltin hydride on the Ar-benzoyl-chloropyridoindolc 363 (Equation 130)... 

Treatment of Baylis-Hillman (BH) derivatives 10, obtained from 3-(2-bromophenyl)-5-methyl-4-isoxazolecarbaldehyde, with tributyltin hydride allowed a straightforward synthesis of isoxazolo-benzazulene systems 11 along with minor amounts of the debrominated products 12 <06TL7043>. BH adducts made from 5-isoxazolecarbaldehydes were converted in moderate yields into pyrrole derivatives by reaction with primary amines and then DBU <06S1021>. 

Tributyltin hydride reduction of carbonyl compounds. The reduction of carbonyl compounds with metal hydrides can also proceed via an electron-transfer activation in analogy to the metal hydride insertion into TCNE.188 Such a notion is further supported by the following observations (a) the reaction rates are enhanced by light as well as heat 189 (b) the rate of the reduction depends strongly on the reduction potentials of ketones. For example, trifluoroacetophenone ( re<1 = —1.38 V versus SCE) is quantitatively reduced by Bu3SnH in propionitrile within 5 min, whereas the reduction of cyclohexanone (Erea — 2.4 V versus SCE) to cyclohexanol (under identical... 

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